The status field is available on the iPhone. It is always displayed on the task details page, but in order to get it on the list page, you need to either sort by status, or have the priority field turned off. This is because the list page shows 2 pieces of information in addition to the sorted value. The two pieces of information are always priority, due-date, status in that order. Thus, if you use both priority and due-date, status will only appear if you sort by status.